UTILITY PLANT AND JOINTLY-OWNED FACILITES (Depreciable Lives of Utility Plant in Service) (Detail)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
TUCSON ELECTRIC POWER COMPANY
Public Utility, Property, Plant and Equipment [Line Items]
Generation Plant	22 years
Transmission Plant	32 years
Distribution Plant	35 years
General Plant	11 years
Depreciation Rate	3.16%		3.22%	3.14%
TUCSON ELECTRIC POWER COMPANY | Electric Generation Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	3.31%	[1]
TUCSON ELECTRIC POWER COMPANY | Electric Transmission Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	1.48%	[2]
TUCSON ELECTRIC POWER COMPANY | Electric Distribution Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	2.08%	[1]
TUCSON ELECTRIC POWER COMPANY | General Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	5.48%	[3]
UNS Electric
Public Utility, Property, Plant and Equipment [Line Items]
Generation Plant	36 years
Transmission Plant	19 years
Distribution Plant	15 years
General Plant	7 years
Depreciation Rate	3.94%		3.99%	4.02%
UNS Electric | Electric Generation Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	2.56%	[2]
UNS Electric | Electric Transmission Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	3.36%	[2]
UNS Electric | Electric Distribution Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	3.97%	[2]
UNS Electric | General Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	8.01%	[2]
UNS Gas
Public Utility, Property, Plant and Equipment [Line Items]
Generation Plant	41 years
Transmission Plant	54 years
General Plant	7 years
Depreciation Rate	2.63%		2.69%	2.84%
UNS Gas | Electric Generation Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	2.37%	[2]
UNS Gas | Gas Transmission Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	1.54%	[2]
UNS Gas | General Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation Rate	4.38%	[2]

[1] In June 2013, the ACC issued the 2013 TEP Rate Order that approved a change in depreciation rates which reflects changes in the remaining average useful lives for our generation, distribution, and general plant assets. See Note 3.

[2] The depreciation rates represent a composite of the depreciation rates of assets within each major class of utility plant.

[3] Unamortized computer software costs were $40 million for UNS Energy and $39 million for TEP as of December 31, 2013, and $36 million for UNS Energy and $35 million for TEP as of December 31, 2012.